This application outlines the design of reagents to improve the sensitivity of immunodiagnostics. Currently, monoclonal or polyclonal antibodies are used and sensitivity is hampered by a low level of amplification in generation of signal output. The investigators propose to use genetic engineering to create potential for greater amplification of signal output. This should raise the sensitivity of immunoassays as well as keep the false positive rate low for diagnostic applications in clinical microbiology, virology, and pathology.